U.S. patent number 8,256,849 [Application Number 12/556,192] was granted by the patent office on 2012-09-04 for braking control device.
This patent grant is currently assigned to Advics Co., Ltd.. Invention is credited to Koichi Kokubo.
United States Patent |
8,256,849 |
Kokubo |
September 4, 2012 |
Braking control device
Abstract
A braking control device which adjusts fluid pressure according
to the degree of opening of a proportional electromagnetic valve
driven at a set drive frequency, and controls a braking force on
the basis of the adjusted fluid pressure, comprises a required
pressure adjustment precision index setting mechanism for setting a
required pressure adjustment precision index on the basis of the
precision of pressure adjustment required when the fluid pressure
is adjusted according to a required braking force, required
operating noise reduction index setting mechanism for setting a
required operating noise reduction index on the basis of a
requirement to reduce operating noise caused by the drive frequency
for driving the proportional electromagnetic valve, and drive
frequency setting mechanism for setting the drive frequency of the
proportional electromagnetic valve on the basis of the set required
pressure adjustment precision index and required operating noise
reduction index.
Inventors: |
Kokubo; Koichi (Nagoya,
JP) |
Assignee: |
Advics Co., Ltd. (Kariya,
Aichi-Pref., JP)
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Family
ID: |
42006561 |
Appl.
No.: |
12/556,192 |
Filed: |
September 9, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100066164 A1 |
Mar 18, 2010 |
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Foreign Application Priority Data
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Sep 12, 2008 [JP] |
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2008-234620 |
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Current U.S.
Class: |
303/119.1;
303/113.1; 303/150 |
Current CPC
Class: |
B60T
8/36 (20130101); B60T 8/4872 (20130101); B60T
8/3655 (20130101) |
Current International
Class: |
B60T
8/38 (20060101) |
Field of
Search: |
;303/20,113.1,114.1,114.3,116.1,119.1,150,153,155,156,168
;251/129.05,129.08 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Williams; Thomas J
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney
PC
Claims
What is claimed is:
1. A braking control device for adjusting a fluid pressure
according to the degree of opening of a proportional
electromagnetic valve driven at a set drive frequency, and
controlling a braking force on the basis of the adjusted fluid
pressure, said braking control device comprising: required pressure
adjustment precision index setting means for setting a required
pressure adjustment precision index on the basis of the precision
of pressure adjustment required when the fluid pressure is adjusted
according to a required braking force; required operating noise
reduction index setting means for setting a required operating
noise reduction index on the basis of a requirement to reduce
operating noise caused by said drive frequency for driving said
proportional electromagnetic valve; and drive frequency setting
means for setting the drive frequency of said proportional
electromagnetic valve on the basis of said set required pressure
adjustment precision index and required operating noise reduction
index.
2. The braking control device according to claim 1, wherein said
drive frequency setting means sets the drive frequency of said
proportional electromagnetic valve to a value that increases with
decreased said set required pressure adjustment precision index, or
increased said set required operating noise reduction index.
3. The braking control device according to claim 1, wherein said
required operating noise reduction index setting means sets said
required operating noise reduction index to a value that increases
with decreased vehicle speed.
4. The braking control device according to claim 1, comprising
frictional coefficient acquiring means for acquiring the frictional
coefficient of a road surface on which the vehicle is positioned;
wherein said required operating noise reduction index setting means
sets said required operating noise reduction index to a value that
increases with decreased said acquired frictional coefficient of
the road surface.
5. The braking control device according to claim 1, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
6. The braking control device according to claim 2, wherein said
required operating noise reduction index setting means sets said
required operating noise reduction index to a value that increases
with decreased vehicle speed.
7. The braking control device according to claim 6, comprising
frictional coefficient acquiring means for acquiring the frictional
coefficient of a road surface on which the vehicle is positioned;
wherein said required operating noise reduction index setting means
sets said required operating noise reduction index to a value that
increases with decreased said acquired frictional coefficient of
the road surface.
8. The braking control device according to claim 7, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
9. The braking control device according to claim 2, comprising
frictional coefficient acquiring means for acquiring the frictional
coefficient of a road surface on which the vehicle is positioned;
wherein said required operating noise reduction index setting means
sets said required operating noise reduction index to a value that
increases with decreased said acquired frictional coefficient of
the road surface.
10. The braking control device according to claim 9, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
11. The braking control device according to claim 2, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
12. The braking control device according to claim 3, comprising
frictional coefficient acquiring means for acquiring the frictional
coefficient of a road surface on which the vehicle is positioned;
wherein said required operating noise reduction index setting means
sets said required operating noise reduction index to a value that
increases with decreased said acquired frictional coefficient of
the road surface.
13. The braking control device according to claim 12, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
14. The braking control device according to claim 3, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
15. The braking control device according to claim 4, comprising
control mode determining means for determining a control mode of
said braking force according to the state of the vehicle; wherein
said required pressure adjustment precision index setting means and
said required operating noise reduction index setting means set
said required pressure adjustment precision index and required
operating noise reduction index on the basis of said determined
control mode of said braking force.
16. A braking control device for adjusting a fluid pressure
according to the degree of opening of a proportional
electromagnetic valve driven at a set drive frequency, and
controlling a braking force on the basis of the adjusted fluid
pressure; said braking control device comprising: vehicle speed
acquiring means for acquiring the speed of the vehicle; and drive
frequency setting means for setting the drive frequency of said
proportional electromagnetic valve to a value that increases with
decreased said acquired vehicle speed.
17. A braking control device for adjusting a fluid pressure
according to the degree of opening of a proportional
electromagnetic valve driven at a set drive frequency, and
controlling a braking force on the basis of the adjusted fluid
pressure; said braking control device comprising: frictional
coefficient acquiring means for acquiring the frictional
coefficient of a road surface on which the vehicle is positioned;
and drive frequency setting means for setting the drive frequency
of said proportional electromagnetic valve to a value that
increases with decreased said acquired frictional coefficient of
the road surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a braking control device for
adjusting a fluid pressure according to the degree of opening of a
proportional electromagnetic valve driven at a set drive frequency,
and controlling a braking force on the basis of the adjusted fluid
pressure.
2. Description of the Related Art
Conventional control devices are known in which an excitation
current is applied to a linear solenoid to control the driving of a
proportional electromagnetic valve, and the object being controlled
is controlled by the proportional electromagnetic valve. In one
application of this technique, a proportional electromagnetic valve
is provided in a braking control device of a vehicle. In such a
braking control device, a predetermined current as a control signal
is fed from a control device to the linear solenoid of the
proportional electromagnetic valve, whereby the proportional
electromagnetic valve actuates and opens and closes an oil channel,
and the flow rate or hydraulic pressure of the oil is adjusted. In
this type of braking control device, noise is sometimes generated
by wide fluctuations in hydraulic pressure between the upstream
side (master cylinder side) and downstream side (wheel cylinder
side) of the proportional electromagnetic valve. Vehicle braking
force maintaining devices (hereinafter referred to as braking force
maintaining devices) have therefore been developed that are capable
of suppressing the occurrence of such noise (Patent Document 1, for
example).
In the braking force maintaining device described in Patent
Document 1, the control frequency of duty control for controlling
the opening and closing of the electromagnetic valve is set to a
low value (20 Hz) when the brake fluid pressure of the channel
downstream from the electromagnetic valve is higher than a
predetermined pressure (3 MPa), i.e., when the braking force that
had been maintained in order to prevent movement of the vehicle is
still large. When the brake fluid pressure of the channel
downstream from the electromagnetic valve is at or below the
predetermined pressure (3 MPa), i.e., when a certain amount of
braking force remains, the control frequency of duty control for
controlling the opening and closing of the electromagnetic valve is
set somewhat high (60 Hz). When the brake fluid pressure of the
channel downstream from the electromagnetic valve has been
adequately reduced (to 0.3 MPa or lower), the control frequency of
duty control for controlling the opening and closing of the
electromagnetic valve is set to an extremely high value (1
kHz).
PRIOR ART DOCUMENTS
Patent Documents
[Patent Document 1] JP (Kokai) 2004-203110 (paragraph No. 0039 and
others)
SUMMARY OF THE INVENTION
In the braking force maintaining device described in Patent
Document 1, when the vehicle starts to move from brake holding
control, i.e., when the brake fluid pressure is released, the
frequency of control of the electromagnetic valve decreases with
increased braking force, as described above. It is therefore
possible to suppress the occurrence of noise generated by wide
fluctuation of the fluid pressure between the upstream side (master
cylinder side) and downstream side (wheel cylinder side) of the
proportional electromagnetic valve. However, the frequency when the
braking force maintaining device described in Patent Document 1
drives the proportional electromagnetic valve by duty control is 20
to 1 kHz, and this frequency range is within the range of
frequencies audible to humans (20 to 20 kHz). The noise is
therefore bothersome to vehicle occupants.
The present invention was developed in view of the problems
described above, and an object of the present invention is to
provide a braking control device whereby operating noise caused by
the drive frequency of the proportional electromagnetic valve can
be reduced without reducing the performance of fluid pressure
control.
In order to adjust a fluid pressure according to the degree of
opening of a proportional electromagnetic valve driven at a set
drive frequency, and to control a braking force on the basis of the
adjusted fluid pressure, the braking control device according to
the present invention for achieving the abovementioned objects
comprises required pressure adjustment precision index setting
means for setting a required pressure adjustment precision index on
the basis of the precision of pressure adjustment required when the
fluid pressure is adjusted according to a required braking force;
required operating noise reduction index setting means for setting
a required operating noise reduction index on the basis of a
requirement to reduce operating noise caused by the drive frequency
for driving the proportional electromagnetic valve; and drive
frequency setting means for setting the drive frequency of the
proportional electromagnetic valve on the basis of the set required
pressure adjustment precision index and required operating noise
reduction index.
Adopting such a characteristic configuration makes it possible to
set the drive frequency of the proportional electromagnetic valve
according to the degree of priority when a degree of precision of
fluid pressure that is in accordance with the braking force is
required, and when reduction of the operating noise is required.
Consequently, it is possible to reduce operating noise that occurs
due to the drive frequency of the proportional electromagnetic
valve, without reducing the performance of fluid pressure
control.
The drive frequency setting means preferably sets the drive
frequency of the proportional electromagnetic valve to a value that
increases with decreased set required pressure adjustment precision
index or increased set required operating noise reduction
index.
Through such a configuration, when a degree of precision of fluid
pressure that is in accordance with the braking force is not
required, or when reduction of the operating noise is required, the
operating noise that occurs due to the drive frequency of the
proportional electromagnetic valve can be reduced by setting the
drive frequency of the proportional electromagnetic valve to a high
value. Consequently, operating noise that is bothersome to vehicle
occupants can be made inaudible.
The required operating noise reduction index setting means
preferably sets the required operating noise reduction index to a
value that increases with decreased vehicle speed.
Through such a configuration, even when the speed of the vehicle is
low and there is minimal travel noise, the drive frequency of the
proportional electromagnetic valve is set to a high value, and
operating noise that occurs due to the drive frequency of the
proportional electromagnetic valve can therefore be made inaudible
to the vehicle occupants.
Frictional coefficient acquiring means is preferably provided for
acquiring the frictional coefficient of a road surface on which the
vehicle is positioned, wherein the required operating noise
reduction index setting means sets the required operating noise
reduction index to a value that increases with decreased acquired
frictional coefficient of the road surface.
Through such a configuration, when the frictional coefficient of
the road surface is small and the vehicle occupant drives more
cautiously, the drive frequency of the proportional electromagnetic
valve is set to a high value, and operating noise that occurs due
to the drive frequency of the proportional electromagnetic valve
can therefore be made inaudible to the vehicle occupants.
Control mode determining means is preferably provided for
determining a control mode of the braking force according to the
state of the vehicle, wherein the required pressure adjustment
precision index setting means and the required operating noise
reduction index setting means set the required pressure adjustment
precision index and required operating noise reduction index on the
basis of the determined control mode of the braking force.
Through such a configuration, a fluid pressure that is in
accordance with the braking force can be precisely set when precise
brake control is needed, such as in a vehicle control mode used
during an emergency, for example. Consequently, it is possible for
the determined control mode to be implemented appropriately. In
such cases as when silence is needed more than precise brake
control, such as when the vehicle occupants are riding in relaxed
fashion, the drive frequency of the proportional electromagnetic
valve is set to a high value, and operating noise that occurs due
to the drive frequency of the proportional electromagnetic valve
can be made inaudible to the vehicle occupants.
In order to adjust a fluid pressure according to the degree of
opening of a proportional electromagnetic valve driven at a set
drive frequency, and to control a braking force on the basis of the
adjusted fluid pressure, the braking control device according to
the present invention for achieving the abovementioned objects
alternatively comprises control mode determining means for
determining a control mode of the braking force according to the
state of the vehicle, and drive frequency setting means for setting
the drive frequency of the proportional electromagnetic valve on
the basis of the control mode determined by the control mode
determining means.
Through such a characteristic configuration, in a specific control
mode used when, for example, the vehicle occupants are traveling in
relaxed fashion, travel noise becomes significant when the vehicle
speed is high, and the operating noise of the proportional
electromagnetic valve is therefore hardly noticeable. Therefore, a
fluid pressure that is in accordance with the braking force can be
precisely set by setting the drive frequency of the proportional
electromagnetic valve to a low value. Since travel noise is low
when the vehicle speed is low, the drive frequency of the
proportional electromagnetic valve can be set to a high value, and
the operating noise of the proportional electromagnetic valve can
be made inaudible to the vehicle occupants.
In order to adjust a fluid pressure according to the degree of
opening of a proportional electromagnetic valve driven at a set
drive frequency, and to control a braking force on the basis of the
adjusted fluid pressure, the braking control device according to
the present invention for achieving the abovementioned objects
alternatively comprises vehicle speed acquiring means for acquiring
the speed of the vehicle, and drive frequency setting means for
setting the drive frequency of the proportional electromagnetic
valve to a value that increases with decreased acquired vehicle
speed.
Through such a characteristic configuration, travel noise becomes
significant when the vehicle speed is high, and the operating noise
of the proportional electromagnetic valve is therefore hardly
noticeable. Accordingly, a fluid pressure that is in accordance
with the braking force can be precisely set by setting the drive
frequency of the proportional electromagnetic valve to a low value.
Since travel noise is low when the vehicle speed is low, the drive
frequency of the proportional electromagnetic valve can be set to a
high value, and the operating noise of the proportional
electromagnetic valve can be made inaudible to the vehicle
occupants.
In order to adjust a fluid pressure according to the degree of
opening of a proportional electromagnetic valve driven at a set
drive frequency, and to control a braking force on the basis of the
adjusted fluid pressure, the braking control device according to
the present invention for achieving the abovementioned objects
alternatively comprises frictional coefficient acquiring means for
acquiring the frictional coefficient of a road surface on which the
vehicle is positioned, and drive frequency setting means for
setting the drive frequency of the proportional electromagnetic
valve to a value that increases with decreased acquired frictional
coefficient of the road surface.
Through such a characteristic configuration, when the frictional
coefficient of the road surface is low, and the vehicle occupant
drives more cautiously, the drive frequency of the proportional
electromagnetic valve is set to a high value, and operating noise
that occurs due to the drive frequency of the proportional
electromagnetic valve can therefore be made inaudible to the
vehicle occupants.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view schematically showing the control blocks of a
brake system to which the braking control device is provided;
FIG. 2 is a view showing the relationship between sound pressure
and the drive frequency of the proportional electromagnetic
valve;
FIG. 3 is a view showing an example of the differential pressure
characteristic of the proportional electromagnetic valve;
FIG. 4 is a view showing the overall structure of the power control
section;
FIG. 5 is a view showing the internal structure of the brake
control unit;
FIG. 6 is a view showing the drive frequency that is set based on
the required pressure adjustment precision index and the required
operating noise reduction index; and
FIG. 7 is a flowchart relating to a process in which the braking
control device controls the brake control unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will next be described based
on the drawings. FIG. 1 is a view schematically showing the control
blocks of a brake system 100 to which the braking control device 1
of the present invention is provided. In the present embodiment,
the braking control device 1 is provided to a vehicle, and the
braking control device 1 adjusts a fluid pressure in accordance
with the degree of opening of a proportional electromagnetic valve
49 (see FIG. 5) driven at a set drive frequency, and controls
braking force on the basis of the adjusted fluid pressure.
The brake system 100 has a control system for augmenting the force
with which a brake pedal 30 is depressed (depressing force) through
the use of a booster 31, transmitting the augmented force to a
tandem-type master cylinder 32, and transmitting the pressure of
brake fluid in the master cylinder 32 from a brake control unit 40
to a brake device BK.
The master cylinder 32 has a structure for simultaneously sending,
in accordance with a brake depression operation, pressurized brake
fluid from one pressurization chamber 32a via a fluid path 33F to
the brake device BK provided to the front wheels, and sending
pressurized brake fluid from another pressurization chamber 32b via
a fluid path 33R to the brake device BK provided to the rear
wheels. The pressure of the brake fluid from the fluid paths 33F,
33R is applied to the brake device BK via the brake control unit
40.
The booster 31 has the functions of augmenting the depressing force
by the action of the vacuum pressure of an engine (not shown) on a
diaphragm (not shown) inside the booster 31 and applying the
augmented force to the master cylinder 32 when the brake pedal 30
is depressed. The master cylinder 32 is in a horizontal
orientation, two pistons (not shown) are arranged concentrically in
tandem inside the master cylinder 32, and pressure is applied to
the brake fluid from the pressurization chamber 32a or 32b that
corresponds to each piston. A reservoir tank 34 for replenishing
the brake fluid in the master cylinder 32 is provided at the top of
the master cylinder 32.
A vehicle wheel speed sensor 21 for detecting the state of the
vehicle, a steering sensor 22, a distance sensor 23, a yaw rate
sensor 24, and a G sensor 25 are also provided to the vehicle.
The vehicle wheel speed sensor 21 monitors the locking state of the
vehicle wheels and detects the speed of the vehicle, and therefore
corresponds to the vehicle speed acquiring means for acquiring the
speed of the vehicle. A vehicle wheel speed sensor 21 having such a
function is provided to the left-front, right-front, left-rear, and
right-rear (hereinafter referred to as FL, FR, RL, and RR,
respectively) wheels of the vehicle. The steering sensor 22 detects
the rudder angle when rotated with respect to the center steering
position. The distance sensor 23 measures the distance to a vehicle
positioned directly in front. The distance sensor 23 has an
ultrasound transmitter and receiver, and measures distance from the
time that elapses between transmission of an ultrasound wave and
detection of the reflected wave. This distance corresponds to the
inter-vehicular distance between the vehicle and a vehicle
traveling in front of the vehicle when the vehicle is moving. The
use of ultrasound is, of course, not limiting, and microwaves or
other electromagnetic waves may be used, or the distance may be
measured optically using infrared lasers or the like. The yaw rate
sensor 24 detects the vehicle speed (angular speed) when the
vehicle is traveling in a curve, and the G sensor 25 detects the
acceleration experienced by the vehicle. This detection of
acceleration is possible not only for acceleration in the
horizontal direction, but for acceleration in the vertical
direction as well. The detection results acquired by the vehicle
wheel speed sensor 21, steering sensor 22, distance sensor 23, yaw
rate sensor 24, and G sensor 25 are transmitted as sensor outputs
to the braking control device 1.
The braking control device 1 is composed of functional sections
that include a control mode determining section 11, a target
hydraulic pressure computation section 12, a current value
computation section 13, a drive frequency setting section 14, and a
power control section 15.
The control mode determining section 11 functions as a control mode
determining means for determining a control mode of the braking
force according to the state of the vehicle. The state of the
vehicle can be specified according to the sensor outputs described
above. The term "control mode" refers to a type of brake control
that is appropriate in order to maintain the safety of the vehicle
when the vehicle is traveling. In the present embodiment, the
control modes are ABS mode, TCS mode, ESC mode, ACC mode, PCS mode,
and REG mode.
The ABS mode is a control mode for preventing the tires from
locking and slipping during sudden braking or brake operation on a
low-friction road. The TCS mode is a control mode for preventing
the tires from skidding when the vehicle accelerates or begins to
move. The ESC mode is a control mode for suppressing sideways
sliding and automatically maintaining the travel direction of the
vehicle when sideways slipping of the vehicle is sensed during
travel on a slippery road or when the steering wheel is turned
suddenly. The ACC mode is a control mode for automatically
adjusting the distance between the vehicle and a vehicle in front.
The PCS mode is a control mode for warning the vehicle occupant of
impending danger using a sound or display, and increasing the
hydraulic pressure of the brake so that the brake is applied merely
by a small depression of the brake pedal 30 when the potential for
collision is determined to be high on the basis of the position of,
or distance to, an obstacle. In the PCS mode, when the brake
hydraulic pressure is increased, and a collision is unavoidable
notwithstanding the warning, the mode automatically forces the
brake to be applied. When the vehicle is a hybrid vehicle, the REG
mode is a control mode for cooperatively controlling a normal
hydraulic brake and a regenerative brake for recovering a battery
by causing a rotary electric motor, which is the drive source
during deceleration or braking, to operate as an electrical
generator and converting the kinetic energy of the vehicle into
electrical energy, and obtaining a braking force that is in
accordance with the depressing force of the brake pedal 30.
The control mode determining section 11 determines the optimum
control mode from among the control modes described above according
to the state of the vehicle, on the basis of the sensor outputs
transmitted from the sensors described above. Consequently, it is
possible to maintain the safety of the vehicle, provide a pleasant
riding experience for the occupants, and ensure the safety of the
occupants.
The target hydraulic pressure computation section 12 computes the
target hydraulic pressure that is necessary for the brake device BK
in order to decelerate or stop the vehicle. Specifically, when the
vehicle is forced out of a curve by centrifugal force while
traveling in a curve, the actual yaw rate is detected as being
smaller than the raw rate that is determined from the speed and the
degree to which the steering is turned. In such a case, control is
performed so that the output of the engine is reduced, braking is
applied, and the disparity with the proper course is reduced. In
such cases as when the vehicle goes into a spin, a yaw rate is
detected that is larger than the yaw rate determined from speed and
centrifugal force. In such a case, the spin can be suppressed by
applying a strong braking force to the outside front wheel. Such
maintenance of stability is utilized not only during travel in a
curve, such as described above, but also during sudden steering to
avoid an obstacle, or when suppressing sideways sliding at such
times as when the vehicle enters a curve on a slippery road
surface.
Although this is described in greater detail hereinbelow, the brake
control unit 40 is also provided with a proportional
electromagnetic valve 49 so as to add to the pressure of the brake
fluid sent from the master cylinder 32, adjust the pressure of the
brake fluid sent by a pump P, and apply the brake fluid to brake
devices BK provided to the vehicle wheels. The proportional
electromagnetic valve 49 is a normally open-type valve that is
controlled from an open-valve state to a closed-valve state in
order to open or block the flow path through which the brake fluid
flows, and the opening and closing of the valve body (not shown) of
the proportional electromagnetic valve 49 is controlled by applying
an excitation current to a linear solenoid 49a (see FIG. 4)
provided to the proportional electromagnetic valve 49. The
excitation current applied to the linear solenoid 49a is determined
by the current value computation section 13 according to the
control mode of braking control as determined by the control mode
determining section 11.
The proportional electromagnetic valve 49 is not merely fully open
or fully closed, but the degree of opening thereof can be finely
adjusted. Consequently, the excitation current computed by the
current value computation section 13 and applied to the linear
solenoid 49a is precisely computed according to the degree of
opening. This excitation current is controlled by DUTY control.
Specifically, the excitation current is determined by ON-DUTY and
OFF-DUTY states. For example, the excitation current is 10 A when
ON-DUTY is 100%, and the excitation current is 3 A when ON-DUTY is
controlled at 30%. When ON-DUTY is controlled at 45%, the
excitation current is 4.5 A. The desired excitation current can
thus be applied by controlling the ON-DUTY. This ON-DUTY control is
performed by the power control section 15 described
hereinafter.
The drive frequency setting section 14 sets the frequency of the
DUTY waveform relating to the DUTY control described above. This
frequency is referred to as the drive frequency because a FET is
driven by inputting this frequency to the gate terminal of the FET,
which is switched in accordance with the DUTY waveform. The drive
frequency used is usually 1 k to 10 kHz. The audible frequency
range is considered to be 20 to 20 kHz. Consequently, the drive
frequency for driving the abovementioned FET is sometimes audible
and unpleasant to the vehicle occupants. FIG. 2 shows the
relationship between such a drive frequency and the sound pressure
of an unpleasant sound. As shown in FIG. 2, the sound pressure
increases with lower drive frequency and decreases with higher
drive frequency. A high drive frequency is thus preferred in order
to reduce the sound pressure (reduce unpleasant sound). FIG. 2
shows a waveform in which the characteristic actually obtained has
been filtered to remove noise.
FIG. 3 is a view showing an example of the differential pressure
characteristic of the proportional electromagnetic valve 49. FIG. 3
shows the relationship between differential pressure and three
patterns of excitation currents for a low-frequency band (e.g.,
less than 3 kHz) in which the drive frequency is relatively low, a
middle-frequency band (e.g., 3 kHz or higher and less than 7 kHz)
in which the drive frequency is medium, and a high-frequency band
(e.g., 7 kHz or higher) in which the drive frequency is high. The
low-frequency band is indicated by a solid line, the
middle-frequency band is indicated by a dashed line, and the
high-frequency band is indicated by a chain double-dashed line. The
differential pressure characteristic of the proportional
electromagnetic valve 49 has hysteresis with respect to all the
frequency bands, as shown in FIG. 3. Specifically, the differential
pressure for the characteristic when the excitation current is
increased differs from the differential pressure for the
characteristic when the excitation current is reduced. Such
hysteresis tends to increase as the drive frequency is increased
(i.e., the width of the hysteresis tends to increase). Furthermore,
when the drive frequency is high, the dither effect (effect whereby
apparent friction decreases due to a minute high-frequency
vibration being imparted in an area of solid friction) decreases,
and the valve body therefore moves less readily. The characteristic
is therefore stepped rather than smooth, as in the case of a low
drive frequency. Given this hysteresis or the stepped
characteristic, it is not easy to appropriately control the
proportional electromagnetic valve 49 so that the hydraulic
pressure of the brake device BK conforms to the target hydraulic
pressure. A low drive frequency is therefore preferred in the
differential pressure characteristic. There is thus a trade-off
between reduction of sound pressure and controllability of the
proportional electromagnetic valve 49 as relates to the drive
frequency.
Returning to FIG. 1, the drive frequency setting section 14
therefore sets the drive frequency with consideration for reduction
of sound pressure and controllability of the proportional
electromagnetic valve 49. Specifically, in conditions in which
precision of pressure adjustment is required, brake performance is
emphasized over operating noise, and the drive frequency is
therefore set low. In conditions in which there is little
requirement for precision of pressure adjustment, and operating
noise may be noticeable to the vehicle occupants, the drive
frequency is set to a high value (as described in detail
hereinafter).
The power control section 15 applies an excitation current to the
linear solenoid 49a on the basis of the current value computed by
the current value computation section 13, and the drive frequency
set by the drive frequency setting section 14. FIG. 4 is a view
showing the overall structure of the power control section 15. The
power control section 15 is provided with a switching control
section 15a and a FET 15b. The switching control section 15a
performs DUTY control so that the current value computed by the
current value computation section 13 is achieved at the drive
frequency set by the drive frequency setting section 14. The DUTY
waveform outputted from this switching control section 15a is
inputted to the gate terminal of the FET 15b.
A power supply B for feeding the excitation current to the linear
solenoid 49a is connected to the drain terminal of the FET 15b.
This power supply B may be a battery provided to the vehicle. One
of the terminals of the linear solenoid 49a is connected to the
source terminal of the FET 15b. The other terminal of the linear
solenoid 49a is grounded. The FET 15b is turned on and a current
flows from the battery B to the linear solenoid 49a when the DUTY
waveform outputted from the switching control section 15a is in the
"High" state. The FET 15b is turned off and a current no longer
flows to the linear solenoid 49a when the DUTY waveform is in the
"Low" state. The power control section 15 applies the excitation
current to the linear solenoid 49a in this manner.
FIG. 5 is a view showing the internal structure of the brake
control unit 40. The brake control unit 40 has a fluid pressure
control section 40F for controlling the pressure of the brake fluid
fed via the fluid path 33F and applying the pressure to the left
front FL brake device BK and the right front FR brake device BK,
and further has a fluid pressure control section 40R for
controlling the pressure of the brake fluid fed via the fluid path
33R and applying the pressure to the left rear RL brake device BK
and the right rear RR brake device BK.
The fluid pressure control section 40F that corresponds to the left
front FL brake device BK and the right front FR brake device BK,
and the fluid pressure control section 40R that corresponds to the
left rear RL brake device BK and the right rear RR brake device BK
have substantially the same structure and operate in the same
manner. The structure and operation of the fluid pressure control
section 40F that corresponds to the left front FL brake device BK
and right front FR brake device BK will therefore be described
below.
The fluid pressure control section 40F is provided with the
normally open-type proportional electromagnetic valve 49 for
causing the fluid pressure from a primary fluid path 41
communicated with the fluid path 33F to act on the left front FL
and right front FR brake device BK. Parallel to the proportional
electromagnetic valve 49, a check valve 50 is provided for allowing
the fluid pressure to escape toward the brake devices BK from the
fluid path 33F when the fluid pressure of the fluid path 33F is
greater than the fluid pressure on the side of the brake devices
BK.
A fluid path 51 is provided on the side of the proportional
electromagnetic valve 49 toward the brake devices BK. A first flow
diversion path 51a and a second flow diversion path 51b are formed
in the fluid path 51. Normally open-type inlet valves 42 are
interposed in the first flow diversion path 51a and second flow
diversion path 51b, and check valves 43 for allowing fluid pressure
to escape toward the fluid path 51 from the brake devices BK are
provided parallel to the inlet valves 42.
Branch fluid paths 51c that branch in positions further toward the
brake devices BK than the inlet valves 42 are formed in the first
flow diversion path 51a and second flow diversion path 51b, and
normally closed-type outlet valves 44 are interposed in the branch
fluid paths 51c.
The inlet valves 42 are composed of electromagnetically operated
two-position switch valves that are open when energized, and closed
when not energized. The outlet valves 44 are composed of
electromagnetically operated two-position switch valves that are
closed when not energized, and open when energized.
A reservoir 45 for temporarily storing brake fluid is provided in
the portion where the branch fluid paths 51c from the two outlet
valves 44 merge, and a return fluid path 46 is provided for
returning the brake fluid from the reservoir 45 to the primary
fluid path 41.
A supply fluid path 52 is also provided, in which are interposed a
pump P driven by an electric motor M so as to draw in the brake
fluid from the merging portion of the branch fluid paths 51c
through which the brake fluid is sent from the two outlet valves 44
and to return the brake fluid to the primary fluid path 41; a
damper chamber 47 for reducing the sound of the brake fluid
discharged from the pump P; and an orifice 48 for limiting the flow
rate of the brake fluid that flows to the fluid path 51.
As described above, the drive frequency setting section 14 sets the
drive frequency of the FET 15b provided to the power control
section 15 according to the control mode of braking control.
Specifically, this drive frequency coincides with the drive
frequency of the proportional electromagnetic valve 49. The drive
frequency setting section 14 sets the drive frequency of the
proportional electromagnetic valve 49 on the basis of a required
pressure adjustment precision index that is set based on the
precision of pressure adjustment required when the fluid pressure
is adjusted according to the required braking force, and on the
basis of a required operating noise reduction index that is set
based on a requirement to reduce the operating noise caused by the
drive frequency for driving the proportional electromagnetic valve
49. The required pressure adjustment precision index is an index
indicating the degree of precision of the fluid pressure according
to the required braking force, and the required pressure adjustment
precision index is set to a high value in control modes in which
precision is required in the fluid pressure. The required pressure
adjustment precision index is set by a required pressure adjustment
precision index setting section (not shown) that functions as the
required pressure adjustment precision index setting means. The ABS
mode, TCS mode, ACC mode, REG mode, and other modes correspond to
control modes in which pressure adjustment precision is
required.
The required operating noise reduction index is an index indicating
the degree to which there is a need to reduce the operating noise
caused by the drive frequency at which the proportional
electromagnetic valve 49 is driven, and the required operating
noise reduction index is set to a high value in control modes in
which reduction of operating noise is required. The required
operating noise reduction index is set by a required operating
noise reduction index setting section (not shown) that functions as
the required operating noise reduction index setting means. The ACC
mode or REG mode corresponds to a control mode in which reduction
of operating noise is required, and states of low-speed control or
keeping the vehicle stopped also correspond to such a control
mode.
The required pressure adjustment precision index and required
operating noise reduction index as described above are specified in
advance as being related to each other in the manner shown in FIG.
6. In FIG. 6, the vertical axis indicates the required pressure
adjustment precision index, and the horizontal axis indicates the
required operating noise reduction index. As shown in FIG. 6, the
drive frequency setting section 14 sets the drive frequency of the
proportional electromagnetic valve 49 to a higher value the lower
the required pressure adjustment precision index is set, or the
higher the required operating noise reduction index is set.
Specifically, the vehicle occupants are generally relaxed in a
state in which the vehicle continues to be stationary, wherein the
required pressure adjustment precision is low and the required
operating noise reduction index is high. It is therefore preferred
in such a control mode that control be performed so that the
operating noise caused by the drive frequency is less audible to
the vehicle occupants. The drive frequency is therefore set to a
high value.
The ABS mode, ESC mode, PCS mode, or TCS mode, in which the
required pressure adjustment precision is high, and the required
operating noise reduction index is low, is generally used in
emergencies, and it is therefore more important that a braking
force that corresponds to the status of the vehicle be generated
regardless of whether the vehicle occupants are relaxed. In such a
control mode, precise control of the pressure adjustment is
preferred even when the operating noise caused by the drive
frequency is audible to the vehicle occupants. The drive frequency
is therefore set to a low value.
Furthermore, the vehicle occupants are generally relaxed in the
case of the ACC mode, the REG mode, or a super-low-speed control
mode in which the required pressure adjustment precision is high,
and the required operating noise reduction index is also high.
Precise control of the pressure adjustment is also required.
Therefore, in such a control mode or control, a midrange drive
frequency is selected that enables a certain degree of pressure
adjustment precision and operating noise reduction to be obtained
at the same time.
The required operating noise reduction index setting section in
this instance sets the required operating noise reduction index to
a higher value the lower the speed of the vehicle. Accordingly, the
drive frequency setting section 14 sets the drive frequency of the
proportional electromagnetic valve 49 to a higher value the lower
the speed of the vehicle. Specifically, in the case of the ACC mode
shown in FIG. 6, for example, the required operating noise
reduction index is set to a higher value in the ACC mode when the
vehicle speed is low than in the ACC mode when the vehicle speed is
high. The reason for this is that when the vehicle speed is high,
the travel noise (engine noise, noise of friction of the tires with
the road, and other noise) tends to be greater than when the
vehicle speed is low, and when the vehicle speed is low, the
operating noise of the proportional electromagnetic valve 49 is
easily heard. Therefore, the drive frequency setting section 14
sets the drive frequency to a high value even when the same control
mode is in effect when the vehicle speed is low.
The required operating noise reduction index setting section sets
the required operating noise reduction index to a higher value the
lower the frictional coefficient of the road surface on which the
vehicle is positioned. Accordingly, the drive frequency setting
section 14 sets the drive frequency of the proportional
electromagnetic valve 49 to a higher value the lower the frictional
coefficient of the road surface on which the vehicle is positioned.
This frictional coefficient is computed from the sensor output
transmitted from the G sensor 25. The G sensor 25 thus corresponds
to the frictional coefficient acquiring means for acquiring the
frictional coefficient of the road surface on which the vehicle is
positioned. In the ABS mode shown in FIG. 6, for example, the
required operating noise reduction index is set to a higher value
the lower the frictional coefficient, and the required operating
noise reduction index is set to a lower value the larger the
frictional coefficient.
As examples of specific drive frequencies, the drive frequency is
preferably set to 7 kHz when the vehicle speed is low, and the
drive frequency is preferably set to 3 kHz when the vehicle speed
is high. The drive frequency is preferably set to 7 kHz when the
frictional coefficient of the road surface on which the vehicle is
positioned is small, and the drive frequency is preferably set to 3
kHz when the frictional coefficient of the road surface on which
the vehicle is positioned is large. Furthermore, when, for example,
the vehicle speed is low, and the road surface on which the vehicle
is positioned has a large frictional coefficient, the drive
frequency is preferably set to a value that is computed using the
average of the drive frequency relating to vehicle speed and the
drive frequency relating to frictional coefficient.
The required pressure adjustment precision index setting section
and the required operating noise reduction index setting section
thus set the required pressure adjustment precision index and
required operating noise reduction index on the basis of the
braking force control mode determined according to the state of the
vehicle. The drive frequency setting section 14 sets the drive
frequency of the proportional electromagnetic valve 49 on the basis
of the control mode determined by the control mode determining
section 11.
The flowchart of FIG. 7 will next be used to describe the process
whereby the braking control device 1 controls the brake control
unit 40. The brake system 100 first initializes (step #01). This
initialization involves initialization of the state of each valve,
and initialization of each functional section of the braking
control device 1.
The braking control device 1 then acquires sensor outputs from the
vehicle wheel speed sensor 21, steering sensor 22, distance sensor
23, yaw rate sensor 24, and G sensor 25 (step #02). When the
braking control device 1 is performing control according to any of
the control modes (step #03: Yes), the current value computation
section 13 computes the excitation current to be applied to the
proportional electromagnetic valve 49 (step #04). In step #03, a
determination is made that control is being performed according to
a control mode when the time that any control mode was determined
to be necessary has passed. The determination is made not only on
the basis of the state in which control is actually being
performed, but also on the basis of a sensor output.
When the control mode currently in effect is the PCS mode or the
ESC mode (step #05: Yes), the drive frequency setting section 14
sets the drive frequency to f.sub.min (step #06). When the control
mode currently in effect is not the PCS mode or the ESC mode (step
#05: No), a drive frequency that is in accordance with the
frictional coefficient is computed (step #08) when control is being
performed according to the ABS mode or the TCS mode (step #07:
Yes). A drive frequency that is in accordance with the vehicle
speed is also computed (step #09). The drive frequency setting
section 14 sets the drive frequency for actually driving the FET
15b from the drive frequency that is in accordance with the
frictional coefficient, and the drive frequency that is in
accordance with the vehicle speed (step #10).
When the control mode currently in effect is not the ABS mode or
the TCS mode (step #07: No), but is the ACC mode or the REG mode
(step #11: Yes), verification is made as to whether the vehicle is
stopped. When the vehicle is stopped (step #12: Yes), the drive
frequency setting section 14 sets the drive frequency to f.sub.max
(step #13). On the other hand, when the vehicle is not stopped in
step #12 (step #12: No), the drive frequency setting section 14
sets the drive frequency to a drive frequency that is in accordance
with the vehicle speed (step #14). When a determination is made in
step #11 that the control mode currently in effect is not the ACC
mode or the REG mode, the process is continued without the drive
frequency being set.
When the drive frequency is set by the drive frequency setting
section 14 in step #06, step #10, step #13, and step #14 as
described above, or when the drive frequency is not set in step #11
(step #11: No), the braking control device 1 sets the opening and
closing state of the inlet valves 42 and outlet valves 44 (step
#15).
The electric motor M is then controlled (step #16), the pump P is
driven, and a failsafe process relating to the control mode is
executed (step #17). The process then returns to step #02 and is
continued. In step #03, when control is not being performed
according to a control mode (step #03: No), a failsafe process is
executed as needed (step #17). The braking control device 1 thus
controls the brake system 100 while reducing the operating noise
that occurs due to the drive frequency of the proportional
electromagnetic valve 49, without reducing the performance of fluid
pressure control.
Other Embodiments
In the embodiment described above, a one motor/two pump type, in
which two pumps P are operated by one electric motor M, is shown in
FIG. 5 as an example of the internal structure of the brake control
unit 40 controlled by the braking control device 1. However, the
present invention is not limited by this configuration. For
example, even in the case of a two-motor/four-pump brake control
unit in which four pumps P are operated by two electric motors M,
the braking control device 1 of the present invention makes it
possible for controllability and operating noise reduction of the
proportional electromagnetic valve 49 to be obtained at the same
time by setting the drive frequency of the proportional
electromagnetic valve 49 according to a braking force control mode
that is determined by the state of the vehicle.
In the embodiment described above, the braking control device 1 of
the present invention is described as being configured so that the
drive frequency setting section 14 sets the drive frequency of the
proportional electromagnetic valve 49 on the basis of a required
pressure adjustment precision index that is set based on the
pressure adjustment precision required when the fluid pressure is
adjusted according to the required braking force, and on the basis
of a required operating noise reduction index that is set based on
a requirement to reduce the operating noise caused by the drive
frequency for driving the proportional electromagnetic valve.
However, the present invention is not limited by this
configuration. It is apparent that a configuration may be adopted
whereby the control mode determining section 11 determines a
braking force control mode according to the state of the vehicle,
and, based on the control mode determined by the control mode
determining section 11, the drive frequency setting section 14 sets
the drive frequency of the proportional electromagnetic valve 49 to
a higher value the lower the speed of the vehicle as acquired by
the vehicle wheel speed sensor 21 as a vehicle speed acquiring
means. Specifically, a configuration may be adopted in which the
drive frequency of the proportional electromagnetic valve 49 is set
to a low value when the vehicle speed is high, and the drive
frequency of the proportional electromagnetic valve 49 is set to a
high value when the vehicle speed is low during control of the
control mode (e.g., the ABS mode). Through this configuration, the
operating noise caused by the drive frequency of the proportional
electromagnetic valve 49 can be made less noticeable even when the
vehicle speed is low, and there is minimal travel noise.
A configuration may also be adopted in which the drive frequency
setting section 14 sets the drive frequency of the proportional
electromagnetic valve 49 to a higher value the smaller the
frictional coefficient of the road surface on which the vehicle is
positioned, as acquired by the G sensor 25 as the frictional
coefficient acquiring means. Through this configuration, when the
frictional coefficient of the road surface is small and the vehicle
occupant is driving with caution, the drive frequency of the
proportional electromagnetic valve is set to a high value, and the
operating noise caused by the drive frequency of the proportional
electromagnetic valve can therefore be made inaudible to the
vehicle occupant.
In the embodiment described above, the required pressure adjustment
precision index and the required operating noise reduction index
are specified in advance as being related to each other in the
manner shown in FIG. 6. A configuration may be adopted in which the
required pressure adjustment precision index and the required
operating noise reduction index are amended according to the type
of vehicle in which the braking control device 1 of the present
invention is mounted. Adopting such a configuration makes it
possible for the braking control device 1 of the present invention
to be utilized in various types of vehicles according to
corrections made to the required pressure adjustment precision
index and the required operating noise reduction index.
In the embodiment described above, the drive frequency of the
proportional electromagnetic valve 49 is described as being set on
the basis of the required pressure adjustment precision index and
the required operating noise reduction index. However, the present
invention is not limited by this configuration. For example, it is
apparent that a configuration may be adopted in which the drive
frequency is amended in conjunction with a resonance frequency of
the proportional electromagnetic valve 49. Adopting such a
configuration makes it possible to more effectively reduce the
operating noise in accordance with the structure of the
proportional electromagnetic valve 49.
* * * * *